Oxime ester compounds having hetroaryl moieties are known in the art. For example in CN103044581A macromolecular photoinitiators their preparation method and application thereof in photocurable compositions are provided. KR1225695B1 discloses α-ketoxime ester compounds as photopolymerization initiators. In KR2013003305A oximino dithiocarbonate compounds, containing furan-2-yl, 3-methylthiophen-2-yl, or 2-methylphenyl group are described as photoinitiators. CN102492060B discloses a diphenyl sulfide oxime ester type photoinitiator which comprises a O or S-containing heterocyclic radical substituted aryl or aryl with at least one substituent containing O or S.
The synthesis of certain iminonaphtho[2,3-b]furan derivatives from their respective carbonyl precursors in the regiospecific and the stereospecific manners are described in Bioorganic & Medicinal Chemistry, Volume: 18, Issue: 14, Pages: 5172-5182. KR2013010621A discloses the preparation of an oxime ester compound by reacting a 9H-carbazole-based compound with dicyclohexylcarbodiimide by a dehydration condensation reaction.
Further oxime ester compounds are for example provided in WO2010/060702 and WO08138724. WO 2004050653 A2 discloses oxime ester photoinitiators with heteroaromatic groups.
Color filters (CF) for LCD and white OLED, which comprise a black matrix and red, green and blue color pixels on a glass substrate, are manufactured by photolithography using radically photopolymerizable resists.
Overcoat layers for LCD are used to planarize a surface of the color filters and enhance orientation of liquid crystal and to prevent ion elution from CF to the liquid crystal. The overcoat is manufactured using a thermosetting resin based on an acrylate resin and/or epoxy resin on the color filter by heating, for example, at 220° C. for 30 min. or in combination with photolithography prior to the post-baking process. Thermal stability, light resistance, adhesiveness, hardness and transparency are required.
Spacer for LCD, which controls a cell gap of the liquid crystal layer in LCD panels, is formed with high positional precision by photolithography using a photosensitive composition. The photospacer is manufactured by photolithography using radically polymerizable resists on overcoat or color filter. After photolithography, the photospacer is baked, for example, at 220° C. for 60 min. to attain thermal stability, mechanical strength, adhesiveness, cell gap controllability and high deformation restorability.
A transparent column spacer has been widely used in the LCD technology, but the transparent spacer disturbs polarized light reducing the contrast ratio. One of a possible solution is to mix with a black colorant not to scatter but to absorb the polarized light, i.e. a black column spacer. Black column spacer is also used in the LCD technology.
Also the passivation layer in the backplane for LCD and OLED can be manufactured by photo lithography, as well as the bank layer/pixel definition layer for OLED. Further the transparent conductive layer for touch panel can be manufactured by photo lithography.
Accordingly, in the market there is a strong demand for higher photosensitive photo initiators in order to reduce the energy consumption, to achieve a shorter tact time for higher productivity and/or more freedom in choice of materials for display application. The photoinitiators to be employed in the photosensitive resins Therefore have to be highly reactive, easy to prepare and easy to handle. For example, in color filter resist applications, highly pigmented resists are required for the high color quality property. With the increase of the pigment content, the curing of color resists becomes more difficult. Hence, photoinitiators having a high sensitivity are required. In addition, also such new photoinitiators must meet the high requirements of the industry regarding properties like, for example, easy handling, high solubility, thermal stability and storage stability. Furthermore the initiators in display applications should contribute to surface smoothness of a pattern, adhesiveness to the substrate etc. Further, easy access to corresponding intermediates for the preparation of the compounds should be given. Thus, there still is a need for photoinitiator compounds providing a perfect balance of the requirements as given above. E.g. an acceptable balance between accessability in view of preparation methods and processes as well as properties of the compound as for example sensitivity, solubility etc.